Designate Servers for Specific Services

In larger applications, there may be reasons to divide the load of running VTScada between more than one server. For example, you may wish to have CPU-intensive services such as the alarm manager handled by one computer while another looks after disk I/O tasks such as logging. Another example is to define primary and secondary servers for the I/O device driver. Load distribution is configured using the advanced tab of the Edit Server Lists dialog.

The following instructions use an existing tag (System Historian) to define a service-specific list. When creating a service-specific list for a driver or Historian, there is an advantage to creating the list first, typing in a name rather than selecting the existing tag. After the list has been created, create the matching tag using the same name. By doing so, you ensure that the service uses the custom server list immediately rather than using the default list for a period of time.

To add a service for which you intend to designate primary and backup servers:

  1. Open the Application Configuration dialog.
  2. Select the Edit Server Lists option from the menu.
  3. Click on the button labeled "Advanced Mode"
  4. Right-click on the node, Server Lists

  1. Click on Add Service-Specific Lists

The Add Service-specific Lists dialog opens

  1. Select the service for which you want to define Primary and Backup Servers.

The example shows a service-specific list being created for the System Historian.

I/O services are selected by the name of the attached Device Driver. These will only appear in the server list while the application is running. Also, the System Historian will be shown in the list only while the application is running

  1. Click on OK.

The service is listed in the menu.

Warning:  Do not leave the configuration in this state. As configured, this means that there is no Primary Server for the System Historian.

  1. Right-Click on the service name to open the context menu.

The Add Workstation-specific or Default List dialog opens

  1. Select the option, "Default for Workstations" and click OK. (1)

The entry Default for Workstations is added to the tree.

  1. Right-click on Default for Workstations

  1. Click on Add Server to List
  2. Select the computer that is to serve as the Primary Server for this service.
  3. Click OK

Repeat the last three steps for the backup servers you want to designate for this service.

  1. Click Apply

(1)It is possible to define a server list that is in effect only for a named workstation.

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